# in the front-end checkout process, on "Shipping Information" step, change event under "Update Address" button from `OnUpdate` to `OnUpdateAjax`
# fill the form, excepting Zip Code
# press "Update Address" button
# confirm, that page after reload displays correct JSON data - {"status": "FAILED","uploader_info": [],"field_errors": {"ShippingZip": "Field is required"}}
# in the front-end checkout process, on "Billing Information" step, change event under "Proceed to preview" button from `OnProceedToPreview` to `OnProceedToPreviewAjax`
# fill the form, excepting Zip Code
# press "Proceed to preview" button
# confirm, that page after reload displays correct JSON data - {"status": "FAILED","uploader_info": [],"field_errors": {"BillingZip": "Field is required"}}